It will be apparent from the following disclosure that the present invention has particular utility in conjunction with four-way type lift-plug valves. It should be borne in mind, however, that the present invention also has utility from the standpoint of rotary lift-plug valves other than four-way plug valves. For purposes of simplicity, however, the invention is described particularly as it relates to four-way plug valve mechanisms, such as may be incorporated into bidirectional meter prover systems.
Plug valves may be classified in three basic groups, i.e. cylindrical plug valves, tapered or conical plug valves and spherical plug valves. Spherical plug valves are commonly referred to as ball valves and are simply rotated 90.degree. to establish the open and closed positions of the valve. Cylindrical plug valves are also opened and closed by simple rotational movement. With regard specifically to tapered plug valves, these may be classified as simple rotary valves, wherein the plug element is simply rotated within the valve body for controlling the flow of movement through the valve mechanism or lift-plug valves wherein the valve element is moved linearly as well as rotated during an operational movement. The present invention specifically concerns valve actuator systems for lift-plug type plug valves.
In order to protect the sealing elements and sealing surfaces of tapered plug valves from excessive wear, lift-plug valves have been developed that are operated by lifting the tapered plug element or shifting it linearly to unseat or separate the sealing element of the plug from the seating surfaces defined within the valve body. After the unseating movement, the plug element is then rotated to the proper position and is then moved linearly in the opposite direction to again seat the sealing element of the plug in sealing engagement with the seating surfaces of the valve body. As the plug element is rotated during operation of the valve mechanism, the sealing element often carried by the plug is not in engagement with any internal seating surfaces and therefore no wear occurs during such movement. The service life of lift-turn type plug valves is therefore materially enhanced by preventing the wear that would otherwise occur during operation. Providing a lift-turn capability for plug valve mechanisms is especially important when large plug valves are employed because of the distance of seal travel that occurs during operational movements.
When four-way type lift plug valve mechanisms are incorporated in meter prover systems, it is necessary for such valve mechanisms to be cycled quite frequently at rapid rates of rotation. It is therefore desirable to provide a plug valve mechanism that does not become excessively worn as the result of rapid, frequent cycling.
In four-way plug valves, the rotary valve element defines a vein like fluid blocking structure that is surrounded by a sealing portion that engages sealing surfaces defined within the valve body. As the rotary valve element is moved between its open and closed positions, at certain positions flowing fluid impinges on the vein like fluid blocking structure and develops a force that tends to rotate the valve element either in the direction of movement by the valve actuator or in a direction opposing the valve actuator. This force development phenomenon is typically referred to as "windmilling" where ham systems are employed for achieving rotation of the valve element within the valve body the forces that develop windmilling phenomenon are applied through connection structure to the valve actuator mechanism. In some cases, the valve actuator camming structure allows a certain amount of lost motion to occur during certain phases of the valve actuation movement. Windmilling forces can cause inadvertent movement of the valve element during such lost motion phases of valve actuation and can cause the rotating valve mechanism to move suddenly because of the valve actuator freedom that is allowed by the lost motion phase of valve actuation. When this occurs, the rotating valve will apply slamming forces to the valve actuator mechanism, thereby causing damage to or excessive wear of the valve actuator parts. It is desirable to provide a valve actuator mechanism that is free from lost motion phenomenon, thereby preventing the development of valve slamming as the result of windmilling. It is also desirable to provide means for insuring that severe inertial forces of the rotating valve element are not transmitted to the valve actuator mechanism in such manner that the actuator mechanism becomes excessively worn or damaged during use. This will insure that the valve actuator will provide extended service life and will facilitate less expensive manufacture of the valve actuator mechanism itself.
Where lift plug type valve mechanisms are employed in conjunction with valve actuators for achieving both linear and rotational movements, it is typically necessary for the power actuation mechanism of the valve actuator to be reversed to achieve one of the opposed linear portions of the movement sequence. Stopping and reversing a valve actuator power mechanism during each cycle of operation obviously develops an adverse condition from the standpoint of wear and serviceability. It is desirable to provide a valve actuator mechanism that includes a power mechanism operable in a single rotary or linear direction in order to achieve complete actuation of lift plug type valve mechanisms.
In view of the foregoing, it is a primary feature of the present invention to provide a novel valve actuator mechanism for lift plug type valves wherein the actuator system provides fully controlled linear and rotational movements without allowing the development of a lost motion condition.
It is a further feature of the present invention to provide a novel valve actuator mechanism for lift turn type plug valves that employs a movement translation mechanism to prevent the development of lost motion during movement between the open and closed positions thereof.
It is also a feature of the present invention to provide a novel valve actuator mechanism for lift-turn type plug valve mechanisms, such as four-way valve mechanisms, wherein a single linear movement of one actuator stem in one direction is translated into a first linear movement of a valve actuating stem, and intermediate rotational movement to reposition the valve element and a subsequent opposite linear movement to reseat the valve mechanism.
Among the several features of the present invention is contemplated a novel valve actuator mechanism for four-way lift-turn type plug valves wherein the actuator mechanism including the power actuator system therefor are filled with a protective fluid medium such as hydraulic oil and fluid interchange between the valve actuator mechanism and the power actuator mechanism is promoted by means of fluid interchange circuitry, thus allowing these mechanisms to be completely filled with the protective fluid medium.
Other and further objects, advantages and features of the present invention will become apparent to one skilled in the art upon consideration of this entire disclosure. The form of the invention, which will now be described in detail, illustrates the general principles of the invention, but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention.